For low-vision persons having a visus of less than about 0.4 special viewing aids have to be used for improving their vision. Among those are, for example, magnifying viewing aids being equipped with a telescopic system. Such viewing aids, thereby, provide a magnified image and, thus, theoretically a better vision, however, in view of the fact that even with small turning movements of the head the angular velocity is increased by the magnification factor, the image becomes blurred due to that movement.
Further, so-called hand scanners have been known as viewing aids. Such scanners are equipped with a magnifying optical system. The recorded image may be viewed via a reading device having a display or screen. The inherent disadvantage of such hand scanners is that an arcuate movement is made due to the manual actuation of the scanner, such that during reading of a text the scanner is moved away from the particular line of the text or the line is even entirely missed. Moreover, a problem occurs to find the beginning of the next text line after the preceding line has come to its end. Although hand scanners have been proposed utilizing roller carriages or linear guide rails, such proposed systems are bulky and heavy.
Further, other devices have been disclosed which use a camera system with a telescopic attachment being all mounted to the head. When doing so, the image provided by the camera is fed to a goggle-type image display device which is also mounted to the head (so-called “head mounted displays”—HMD). The disadvantage of these prior art systems is that the image is also blurred in case the head makes jitter movements. If a low-vision person reads a text with such a system and follows the text line with a turning movement of the head, the superimposed jitter movement results in a substantial reduction of reading ability.
From document U.S. Pat. No. 6,731,326 B1, mentioned at the outset, a viewing aid in various different embodiments has been known.
According to a first embodiment, a stationary camera is used that may be pivoted and zoomed by means of a manual control device. The image recorded by the camera is shown on a screen of a television set. This embodiment, therefore, may only be used for scanning stationary objects and, hence, may only be used in a stationary mode.
According to a second embodiment, the person carries a sensor (so-called “head mouse”) at his/her head which allows to control a cursor on a screen by moving the head, in order to mark a particular detail of an object to be magnified. This embodiment, too, is stationary, and its main purpose is to view images.
According to a third embodiment, the person carries a goggle-type image display device as well as a camera. By means of a manual control device, the camera is pivoted and zoomed and the image recorded by the camera is shown in the image display device. This embodiment is intended to be used for mobile purposes, however, it has the already above-mentioned disadvantage, that jitter movements of the head are immediately transferred to the camera, and, hence, deteriorate the quality of the recorded images. This embodiment is, therefore, improper for reading texts.
Document U.S. Pat. No. 6,084,556 A1 discloses a virtual computer monitor. In one embodiment of the monitor (FIG. 6) a video camera is provided for recording an image of an object. The camera is connected to a personal computer (PC) having a conventional WINDOWS?-surface. A person carries an image display device at his/her head, as well as a sensor for sensing head movements. The image display device and the sensor are interleaved via a software of the PC. By means of that software, the person may determine by appropriate movement of his/her head, which detail within the image recorded by the video camera he/she would like to view, for example by means of scrolling. All this happens in real time, i.e. synchronously.
Document U.S. Pat. No. 5,629,988 A1 discloses a system and a method for electronically stabilizing an image, for example an image of a video camera. When doing so, the movement of the video camera is sensed by means of a sensor, and the sensor signal is used for stabilizing the image. By doing so, unwanted jitter movements may be compensated for, which would generate a local displacement of the video camera between two recorded images.